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| Dissertation / PhD Thesis | FZJ-2014-00480 |
2013
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-867-9
Please use a persistent id in citations: http://hdl.handle.net/2128/5802
Abstract: The interplay between the molecular configuration and the electrical and optical properties of various individual nanostructures is studied in this thesis. These are carbon nanotubes (CNTs), tetramanganese-decorated carbon nanotubes, and InAs nanowires that are investigated on the single-device level with high-resolution transmission electron microscopy and spectroscopy (HR-TEM), Raman scattering, and low-temperature quantum transport measurements. These techniques probe complementary material properties and can jointly provide a comprehensive characterization of the individual nanostructure. This correlation is achieved on a novel sample design developed in the course of this thesis. It combines various lithographic steps on a TEM membrane and is compatible with many (self-assembled) nanostructures. It decouples the device from the substrate, leading to clean transport properties. An individual triple-walled carbon nanotube, as identified using HR-TEM, is investigated with Raman spectroscopy and room-temperature electrical transport. The optical response and the transport channel can be assigned to the individual walls. Quantum transport experiments are performed on two additional carbon nanotube devices, identified with the HR-TEM as a two-fold bundle of single-walled CNTs and a triplewalled CNT, respectively. The stability diagrams exhibit complex features as avoided crossings, Fano-shaped coulomb peaks, and regular saw tooth patterns. Their origin is only found with the detailed knowledge of about the atomic structure. More precisely, these features can be modeled with capacitive and molecular interactions between the various elements of the devices and the environment. Universal conductance fluctuations and the phase-coherence length of four individual InAs nanowire transport devices are likewise studied. Two different temperature dependences can be measured. They are not related to a crystal phase mixing because all four nanowires are statistically identical in these terms as determined by a HR-TEM measurement. The properties of carbon nanotubes can be modified by chemical functionalization. The route proposed in this thesis is the decoration with a tetramanganese molecular antiferromagnet via a carboxylate ligand exchange with the carbon nanotube. The degree of functionalization can be controlled with the oxidation of the CNT. The decoration is monitored with bright- and dark field HR-TEM as well as energy-dispersive X-ray and electron energy loss spectroscopy that show the repartition of the Mn on the carbon nanotubes. Raman spectroscopy and SQUID measurements provide further evidence of a successful decoration and show the integrity of the hybrids. Transport experiments on functionalized carbon nanotube networks demonstrate the integrability of such structures into single-hybrid quantum transport devices. In conclusion, the developed sample layout has a great potential to investigate the impact of specific structural modifications on optical and electrical properties of individual nanostructures. This is an important ingredient for the comparison of theoretical predictions and experimental results.
Keyword(s): Dissertation
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